A resistive touch screen is a sensor that translates a physical location of a touch at a point (X, Y) in a rectangular area into a voltage that represents the X and Y value. Such a screen can use four wires, five wires, seven wires or eight wires for generating screen-bias voltages and reading back the voltage at the touch point.
FIG. 1 schematically illustrates a structural diagram of a resistive touch screen. The resistive touch screen includes a first resistive layer 11 and a second resistive layer 12. A first electrode X1 and a second electrode X2, which are parallel with each other, are disposed on two opposite edges of the first resistive layer 11 respectively. A third electrode Y1 and a fourth electrode Y2, which are parallel with each other, are disposed on two opposite edges of the second resistive layer 12 respectively. The third electrode Y1 and the fourth electrode Y2 are perpendicular to the first electrode X1 and the second electrode X2.
When the resistive touch screen suffers a stress strong enough from single-touch, the first resistive layer 11 may be brought into contact with the second resistive layer 12, where an equivalent circuit is illustrated in FIG. 2. The resistance from the first electrode X1 to a contact point between the two resistive layers is equivalent to a resistor R10, the resistance from the second electrode X2 to the contact point between the two resistive layers is equivalent to a resistor R20, the resistance from the third electrode Y1 to the contact point between the two resistive layers is equivalent to a resistor R30, the resistance from the fourth electrode Y2 to the contact point between the two resistive layers is equivalent to a resistor R40, and the single-contact resistance between the first resistive layer 11 and the second resistive layer 12 is equivalent to a contact resistor Rt. In order to measure a coordinate of the touch point in a certain direction on the resistive touch screen, it is necessary to bias one of the two resistive layers. Specifically, a biasing process may include: connecting the first electrode X1 to a reference voltage, connecting the second electrode X2 to ground, and connecting the third electrode Y1 or the fourth electrode Y2 to an input terminal of an Analog-to-Digital Converter (ADC). In this manner, a resistive surface of the first resistive layer 11 is divided into the resistor R10 and the resistor R20 in a direction of X-axis. The voltage of resistor R20 is proportional to a distance between the touch point and the second electrode X2. Thus, an X coordinate of the touch point may be calculated. Similarly, by biasing the second resistive layer 12 and reading the voltage of the first electrode X1 or the second electrode X2, a Y coordinate of the touch point may be calculated as well. However, when there is more than one touch point, none coordinates of the touch points can be obtained by the above methods.
A resistive touch screen which can identify multi-touch points is provided in a PCT patent publication No. WO2009/038277A1. The resistive touch screen includes a first resistive detection pattern and a second resistive detection pattern, both of which have a plurality of parallel stripes. The plurality of parallel stripes in the first resistive detection pattern are perpendicular to those in the second resistive detection pattern. And voltages are alternately applied to some stripes of the first resistive detection pattern and the second resistive detection pattern which are touched to obtain X and Y coordinates.
However, when the above resistive touch screen is employed to detect multi-touch points, the structure of the touch screen needs to be changed, which increases the cost of manufacturing the touch screen.